Population status of the Orinico crododile in Venezuela

360 A.E. Seijas, C. ChaÂvez / Biological Conservation 94 (2000) 353±361
The Orinoco crocodile population in the CRS is not
uniformly distributed. Di€erences in size and structure
were observed among the several river reaches that were
surveyed from 1991 to 1997. The highest densities were
found in CAS, a stretch of the CRS that maintains its
meandering condition and is still surrounded by forest.
This result is in general agreement with data reported by
AyarzaguÈ ena (1987) for the same location. Densities of
crocodiles decrease upstream in CAN and CON, areas
that are a€ected by deforestation, channelization and
contamination (Seijas, 1998).
Our results for SUC and CUL sections represent the
®rst data on the population status of crocodile at these
localities. Here, the Orinoco crocodile population is
extremely low, particularly near Sucre. These river sections
are the only ones of the study area that are navigable
year-round. There is commercial and subsistence
®shing and, possibly illegal caiman hunting, around
Sucre and in La Culebra. Accidental or intentional killing
of Orinoco crocodiles by people may prevent the
recovery of the species crocodile in these areas, although
we did not obtain direct evidence of this.
If data from SUC and CUL are removed, densities of
crocodiles in the CRS are very high (from 3.08 to 7.43
ind./km) compared to these reported by Thorbjarnarson
and Herna ndez (1992) for the Tucupido (before it was
dammed) and the Capanaparo rivers (1.94 and 1.64 ind/
km, respectively). These contrasting ®gures are paradoxical
because, compared to the CRS, the Capanaparo
river is relatively isolated from important human settlements
and is regarded as good crocodile habitat by
Thorbjarnarson and Herna ndez (1992). However, egg
predation and collection of hatchlings by humans,
management problems known from the Capanaparo
river (Thorbjarnarson and Herna ndez, 1992), are factors
of marginal importance in the CRS (Gonza lez-
Ferna ndez, 1995).
Population structure di€ered among river sections.
CON and CAN were dominated by small crocodiles
(less than 1.2 m in TL), which accounted for 56.2% of
the crocodiles seen. In contrast, the crocodile population
in CAS was composed largely of sub-adults and
adults (>1.8 m in TL). CAM showed an intermediate
population structure. These dissimilarities may be partially
explained by di€erences in habitat quality among
sections. The principal nesting beaches are found in
CAS (Seijas, 1998). Di€erences in mortality may also
play a role in structuring these populations. The injury
rate of juvenile crocodiles is lower in northern sections
than in the southern sections of the CRS, which may
indicate a higher risk of predation in southern localities
(Seijas, 1998).
An alternative explanation for di€erences in population
structure among localities is that sites composed
predominantly of juveniles (CON and CAN) may be
recovering from overexploitation (Webb and Messel,
1978; Rebelo and Magnusson, 1983). In the case of
CAN it is more plausible to think that the Orinoco
crocodile is simply colonizing that river stretch. Most of
CAN is an arti®cial channel which has received the
water of the Cojedes river only since the 1960s (PedranÄ
ez 1980; Campo and RodrõÂ guez, 1995).
Finally, population structures may be shaped by
human activities. Large crocodiles are more conspicuous
and probably more frequently killed by people.
Areas surrounding CON and CAN are more developed
and encounters betwee human and crocodiles may occur
with increased frequency. Fewer adults could remain in
the river under these circumstances, and the less conspicuous
juveniles may escape detection, although at
lower densities than juveniles at CAS. In river sections less
accessible to humans, such as CAS, large crocodiles may
have greater chances to survive and became established as
a reproductive population.
The procedures reported here and the population
indices derived from them, represent the ®rst attempt to
standardize methodology for the study of the Orinoco
crocodile population in the CRS, the most important
population of this endangered species. These results
serve as a baseline for future investigation of the species
in the area.
Acknowledgements
This study was made possible by a grant from the
Wildlife Conservation Society (WCS). Satellite images
were generously donated by U. S. Geological Survey
(EROS Data Center). Coromoto RamõÂ rez, Jevert GonzaÂ
lez and Eddy Escalona served as our guides on many
occasions. We appreciate also the hospitality o€ered by
Pedro Rojas, Jose Rodrõ guez, and Jose Caicedo at the
MARNR station in Toma Cojedes, San Rafael de Onoto.
Early versions of the manuscript were reviewed by F. W.
King, John Thorbjarnarson, Richard Bodmer, Melvin
Sunquist, and George Tanner. Robert Godshalk, Craig
Guyer and two anonymous reviewers made important
contributions to the improvement of the paper.
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